Systems and methods for monitoring and/or controlling short-pulse laser welding

Abstract

Systems and methods may be used to monitor and/or control a short-pulse laser welding process involving the formation of a series of heat stakes in the welded materials. The systems and methods use an imaging system, such as an ICI system, capable of obtaining measurements inside the vapor channels during formation of the heat stakes and thus provide stake measurement data representing characteristics of the stakes. The stake measurement data may be used to monitor and/or control the short-pulse laser welding process.

What is claimed is: 
     
         1 . A system for performing a short-pulse laser weld process and monitoring and/or controlling the short-pulse laser weld process, the system comprising:
 a pulsed laser source configured to generate a process beam for performing the short-pulse laser weld process at a weld site for joining at least first and second workpiece materials, wherein the pulsed laser source is configured to generate the process beam with a pulse width and a repetition rate such that the process beam is capable of penetrating at least the first workpiece material and capable of generating a series of vapor channels extending into the second workpiece material, wherein each vapor channel of the series of vapor channels subsequently refills to form a stake in a series of stakes extending into the second workpiece, and wherein a series of pulses of the process beam forms each of the vapor channels and each of the stakes, and wherein the pulse width is less than 1000 ns;   an imaging system configured to generate an imaging beam for reflection at the weld site, to produce an interferometry output from the reflection of the imaging beam, and to detect the interferometry output to produce measurement data representing characteristics of the weld site, wherein the measurement data includes at least stake measurement data representing characteristics of the stakes in the series of stakes extending into the second workpiece material;   a beam delivery system coupled to the pulsed laser source and the imaging system for directing the process beam and the imaging beam to the weld site on the first workpiece; and   a computerized system programmed to receive the measurement data from the imaging system and to monitor and/or control the short-pulse laser weld process based on the measurement data.   
     
     
         2 . The system of  claim 1 , wherein the repetition rate is greater than 10 kHz. 
     
     
         3 . The system of  claim 1 , wherein the imaging system is an inline coherent imaging (ICI) system configured to produce the imaging beam in line with the process beam. 
     
     
         4 . The system of  claim 1 , wherein the pulsed laser source is a nanosecond infrared fiber laser. 
     
     
         5 . The system of  claim 1 , wherein the beam delivery system is configured to continuously translate the process beam across the first workpiece material at a speed in a range of 10 mm/s to 2000 mm/s. 
     
     
         6 . The system of  claim 1 , wherein the beam delivery system includes a scanner configured to deflect and scan the process beam and the imaging beam across the first workpiece material. 
     
     
         7 . The system of  claim 1 , wherein the beam delivery system includes a first mirror for deflecting the imaging beam and a second mirror for deflecting the process beam, wherein the second mirror is a dichroic mirror. 
     
     
         8 . The system of  claim 1 , wherein the beam delivery system includes adjustable deflection elements configured to scan both the process beam and the imaging beam together and configured to scan the imaging beam relative to the process beam for adjusting alignment of the imaging beam relative to the process beam. 
     
     
         9 . The system of  claim 1 , wherein the measurement data includes surface measurement signal data representing a reflection of the imaging beam from a surface of the first workpiece material. 
     
     
         10 . The system of  claim 9 , wherein the computerized system is configured to monitor the short-pulse laser weld process using the surface measurement signal data. 
     
     
         11 . The system of  claim 9 , wherein the computerized system is configured to control the short-pulse laser weld process by adjusting alignment of the imaging beam relative to the process beam in response to the surface measurement signal data. 
     
     
         12 . The system of  claim 9 , wherein the computerized system is configured to control the short-pulse laser weld process by selecting a focal spot size of the process beam based on the surface measurement signal data. 
     
     
         13 . The system of  claim 1 , wherein the computerized system is configured to compare the stake measurement data with previously stored stake measurement data representing characteristics of stakes formed during a reference process, and based on the comparison, to determine if the short-pulse laser weld process conforms to the reference process. 
     
     
         14 . The system of  claim 13 , wherein the stake measurement data represents at least one stake characteristic selected from a group consisting of statistical distribution of a number of stakes formed, frequency of stakes formed, and depth of stakes formed. 
     
     
         15 . The system of  claim 1 , wherein the stake measurement data represents at least one stake characteristic selected from a group consisting of statistical distribution of a number of stakes formed, frequency of stakes formed, and depth of stakes formed. 
     
     
         16 . The system of  claim 1 , wherein the stake measurement data represents at least a frequency of stakes formed, and wherein the computerized system is configured to control a duty cycle and frequency of the process beam in response to the frequency of stakes formed. 
     
     
         17 . A method of performing and monitoring a short-pulse laser weld process, the method comprising:
 generating a process beam having a pulse width less than 1000 ns;   generating an imaging beam;   directing the process beam and the imaging beam to a weld site on a workpiece including at least first and second workpiece materials such that the process beam generates a series of vapor channels extending into the second workpiece material, wherein each vapor channel of the series of vapor channels subsequently refills to form a stake in a series of stakes extending into the second workpiece, and wherein a series of pulses of the process beam forms each of the vapor channels and each of the stakes;   producing an interferometry output from a reflection of the imaging beam from the weld site; and   detecting the interferometry output to produce measurement data representing characteristics of the weld site, wherein the measurement data includes at least stake measurement data representing characteristics of the stakes in the series of stakes extending into the second workpiece material.   
     
     
         18 . The method of  claim 17 , wherein the process beam is generated with a repetition rate greater than 10 kHz. 
     
     
         19 . The method of  claim 17 , wherein the process beam is generated with a repetition rate in a range of 20 to 1000 kHz. 
     
     
         20 . The method of  claim 17 , wherein the process beam is generated with a pulse width in a range of 1 to 1000 ns. 
     
     
         21 . The method of  claim 17 , wherein directing the process beam and the imaging beam include translating the process beam and the imaging beam across the first workpiece material such that the process beam forms each of the vapor channels and each of the stakes as the process beam is translated. 
     
     
         22 . The method of  claim 21 , wherein the process beam is translated across the first workpiece material at a speed in a range of 10 mm/s to 2000 mm/s. 
     
     
         23 . The method of  claim 21 , wherein translating the process beam and the imaging beam across the first workpiece material includes scanning the process beam and the imaging beam across the first workpiece material. 
     
     
         24 . The method of  claim 21 , wherein translating the process beam and the imaging beam across the first workpiece material includes moving the workpiece relative to the process beam and the imaging beam. 
     
     
         25 . The method of  claim 17 , further comprising monitoring the short-pulse laser weld process using the measurement data. 
     
     
         26 . The method of  claim 25 , wherein the measurement data includes surface measurement signal data, and wherein the short-pulse laser weld process is monitored using the surface measurement signal data. 
     
     
         27 . The method of  claim 17 , further comprising controlling the short-pulse laser weld process based on the measurement data. 
     
     
         28 . The method of  claim 27 , wherein the measurement data includes surface measurement signal data, and wherein the short-pulse laser weld process is controlled by adjusting alignment of the imaging beam relative to the process beam using the surface measurement signal data. 
     
     
         29 . The method of  claim 27 , wherein the measurement data includes surface measurement signal data, and wherein the short-pulse laser weld process is controlled by selecting a focal spot size of the process beam based on the surface measurement signal data. 
     
     
         30 . The method of  claim 17 , further comprising comparing the stake measurement data with previously stored stake measurement data representing characteristics of stakes formed during a reference process, and based on the comparison, determining if the short-pulse laser weld process conforms to the reference process. 
     
     
         31 . The method of  claim 30 , wherein the stake measurement data represents at least one stake characteristic selected from a group consisting of statistical distribution of a number of stakes formed, frequency of stakes formed, and depth of stakes formed. 
     
     
         32 . The method of  claim 17 , wherein the stake measurement data represents at least one stake characteristic selected from a group consisting of statistical distribution of a number of stakes formed, frequency of stakes formed, and depth of stakes formed. 
     
     
         33 . The method of  claim 17 , wherein the stake measurement data represents at least a frequency of stakes formed, and further comprising controlling a duty cycle and frequency of the process beam in response to the frequency of stakes formed. 
     
     
         34 . The method of  claim 17 , wherein at least the first workpiece material is a reflective metal and has a thickness less than 0.5 mm. 
     
     
         35 . The method of  claim 17 , wherein the first and second workpiece materials are dissimilar metals.